DG, the way I understand it, there are ads attached to promoted listings, and they appear in the right hand frame of the search results page.  If one of your promoted items appears as an ad on a search result page, that is an impression, if the searcher then clicks that ad, then that is a click.  It doesn't matter where your items actually appear in the search results, if your "bid", as in the amount you agree to pay, is high enough your ad can appear on page one even if your actual listing doesn't apear until page ten.  That is how it works on the other site I use, and from reading all the info I understood it to work the smae here, but I may be wrong.